Having doubt with viruses?

Computer viruses are small software programs that are designed to spread from one computer to another and to interfere with computer operation. A virus might corrupt or delete data on your computer, use your e-mail program to spread itself to other computers, or even erase everything on your hard disk. Viruses are most easily spread by attachments in e-mail messages or instant messaging messages. That is why it is essential that you never open e-mail attachments unless you know who it's from and you are expecting it. Viruses also spread through downloads on the Internet. They can be hidden in illicit software or other files or programs you might download. Viruses can be disguised as attachments of funny images, greeting cards, or audio and video files. To help avoid viruses, it's essential that you keep your computer current with the latest updates and antivirus tools, stay informed about recent threats.

it is a small piece of code..that does it work properly... it is on d hands of the programmer to write on their wish....

virus : a small progarmme that is written by great mind which breaks up any particular software or port n infect your system ! virus are generally created by people who are master in programming n computing !!